Method of cleaning metals



till

Patented Nov. 24, 1931 UNITED STATES PATENT OFFICE HARRY S. GEORGE, OF MASSAZPEQUA, NEW YORK, ASSIGNOR TO ELECTED METAL- LUBGICAL COMPANY, A CORPORATION OF WEST VIRGINIA METHOD OF CLEANING METALS No Drawing.

My invention relates to the cleaning of metals and especially to the treatment of metals which are coated with thin films of oxide so as to produce brightened surfaces having the characteristic color of the metal.

time of the objects of my invention is to remove oxide films without materially atta king the metal so that the metal will pret a suitable foundation for the purpose of oldering, plating or other surfacing processes or so that the metal will present a clean brightened metallic appearance without Application filed June 19,

' nrther processing.

Another object of my invention is to provide methods of cleaning metals which will not leave a residue of corrosion-producing substance on the cleaned metal.

According to my invention,the filmed metal is treated with pyrophosphoric acid. The films are removed from certain metals at temperatures as low as roomtemperatures but higher temperatures are required for some metals. Temperatures up to about 300 C. may be used for a short time but temperatures between 160 C. and 250 C. are sufficiently high to brighten almost all metals. The use of temperatures not greatly in excess of those required to remove the film of ox1de and brighten the metal has a negligible roughening action on metals, and excesslve temperatures are preferably avoided.

As a specific example of my invention, a thin coating of pyrophosphoric acid was placed on a smooth strip of rustless iron which had a thin film of oxide on its surface. The iron was heated to 160 C. to 200 C. and then washed in water. The cleaned iron was perfectly smooth and unetched and the characteristic color of the metal was produced by the treatment.

Only a thin coating of the acid is all that is usually required. Where highly resistant films are treated and temperatures above room temperatures are required, the acidcoated metal may be heated or the metal may be heated and then placed in the acid so that only a thin film of the acid is heated to the required temperature. Instead of heating the metal, the bath may be heated and the 1929. Serial No. 372,221.

colg metal may be treated with the heated acl It is not always necessary for good results to use materials consisting entirel of pyrophosphoric acid. Phosphoric acids aving a content of water less than that corresponding to orthophosphoric acid and more than that corresponding to metaphosphoric acid may be used. Significant amounts of these acids mixed with non-deleterious and inactive'substances may also be used.

A suitable substance for carrying out my process may be made by heating orthophosphoric acid, P O 3H O, to about 160 C. untilthe melt has a water content intermediate the formula, 1 0 -311 0 which contains 0.3800 parts of 'molecularly combined water by weight per part of P 0 and P O -H O which contains 0.1267 parts of molecularly combined water by weight per part of P 0 The substance may also formed by adding water to phosphoric anhydride or .metaphosphoric acid. These acids and pyrophosphoric acid alone have I. cleaning and brightening action at the above mentioned temperatures as distinguished from the coating action of 85% commercial phosphoric acid or of water solutions of phosphoric acids.

After the cleaning material has acted upon the filmed metal, the excess of cleaning material and the oxide film material may be removed from the metal by washing in water or other suitable solvent. The washed and cleaned object has the characteristic color of the metal of which it is composed. The tendency of the cleaned metal to oxidize is extremely feeble since the treatment appears to create a passive condition of the metal with respect to the formation of oxides and this condition remains for a considerable time. i

The above described process is especially useful for cleaning iron, copper, nickel, zinc and alloys containing substantial amounts of these metals and particularly the alloys of iron and chromium. The best temperatures for cleaning and brightening carbon steel are 190 C. to 250 C. Iron-chromium alloys may be cleaned and brightened at 160 C. to 200 C. while copper may be brightened at temperatures as low as ordinary room temperatures.

I claim as my invention:

5 1. The method of brightening oxide coated metal which comprises heating the metal to 160 C. to 300 C. in the presence of a pyrophosphoric acid containing substance.

2. The method of cleaning oxide films 10 from metal articles which comprises coating the articles with a substance comprising pyrophosphoric acid, heating in contact with the substance to at least 160 C. to free the films from the metal and removing the freed 16 films and the excess of cleaning substance.

3. The method of removing oxide coatings from metal articles which comprises treating the articles with a substance comprising pyrophosphoric acid, said substance 80 containing less than 0.3800 and more than 0.1267 parts by weight molecularly combined water per part of P 0 4. The method of removing oxide coatings from metal articles which comprises 2 treating the articles with a substance which contains a phosphoric acid, said acid being composed substantially of pyrophosphoric acid, the water content of said phosphoric acid being less than 0.3800 and more than 0.1267 parts by weight of molecularly combined water per part of P 0 5. The method of cleaning oxide films from metal articles which comprises coating the articles with a substance comprising 35 a pyrophosphoric acid containing less than 0.3800 and more than 0.1267 parts by weight of molecularly combined water per part of P heating to free the films from the metal, and removing the freed films and the excess of cleaning substance.

6. The method of removing oxide coatings from metal articles which comprises applying pyrophosphoric acid.

7 The method oiiremoving oxide coatings from metal articles which comprises applyin pyrophosphoric acid and heating.

n testimony whereof, I aifix my signature.

HARRY S. GEORGE. 

